This is for my sister's hamster btw (and she said she wants to get 3 girl mice because my niece loved the ones I had). I told her we could make a big bin cage, but she doesn't like how they look. He's currently in this cage:

There are some pretty slick bin cages, maybe you could show her some pictures of them on the internet that are well made so she can see that they can look good. You could use colorful translucent plastic and it would look nice.

Also, I'd try to reason with her that what's better for the hamster is what she should be caring about, rather than what is visually pleasing.